1. Field of the Invention
This invention relates to a soldering iron which uses a two-lead type heater-sensor complex comprising a heater unit and a sensor unit as integrated. More particularly, the invention relates to a soldering iron superb in tip temperature control function and free from high-frequency noise.
2. Description of the Related Art
As an example of methods of controlling soldering iron tip temperatures, U.S. Pat. No. 5,043,560 is known. Using the "pulse width control method," this invention varies the power supply time for a soldering iron within a range of 0-100% in half cycle of AC voltage.
Effecting temperature control in every half cycle(H.apprxeq.8.3 mS), this invention is superior in follow-up, but has the following disadvantage:
Wave forms as shown in FIG. 11 are produced in accordance with tip temperatures, and so voltage supplied to the heater is suddenly brought into "ON" state from "OFF" state. This causes high-frequency noise. The nearer to H/2 is the power supply time(H-T), the larger is the high-frequency noise. So even if DC voltage is supplied to the heater, this defect cannot be remedied as long as the pulse width method is used.
Designed to overcome the above disadvantage, the present invention proposes a novel method for controlling the temperature of a soldering iron tip to replace the foregoing pulse width control method. The present invention also proposes a soldering iron having the desired tip temperature control function and the least high-frequency noise.